Google Analytics tracks now Google audio ads as well:
"Google Audio Ads advertisers can now see how their campaign metrics for impressions, ad plays, markets, and CPM correlate with their website traffic data provided by Google Analytics, such as conversions, revenue, and transactions. Customers can see if their audio campaigns resulted in greater amounts of traffic and conversions on a regional basis."

Not much to add, besides that all ad agencies should be aware of where Google is heading. The comission dollars are moving slowly but steadily towards Mountain View